Consumable electrode melting using a centrifugal cast electrode

ABSTRACT

A method for producing a metal ingot, which comprises the steps of: centrifugally casting metal into a consumable electrode; arranging the consumable electrode within a consumable electrode furnace structure; connecting the consumable electrode to a power supply; melting the consumable electrode in a protective environment by passing electrical current between it and a second electrode; and casting the molten metal into an ingot.

United States Patent Tommaney et al.

[151 3,656,535 [4 1 Apr. 18, 1972 [72] Inventors: Joseph W. Tommaney, Valencia, Pa.;

Francis L. Muscatell, Loudonville, NY.

[73] Assignee: Allegheny Ludlum Industries, Inc., Pittsburgh, Pa.

[22] Filed: Nov. 5, 1970 [21] Appl. No.: 87,335

[51] Int. Cl. ..B22d 27/0 2, B22d 13/00 [58] Field of Search ..13/l8; 164/52, 114, 252, 286, 164/298; 75/10 C [56] References Cited UNITED STATES PATENTS 2,640,860 6/1953 Herres et a1 ..l3/ l8 X 2,890,109 6/1959 Cooper ..13/l8 X 2,899,294 8/1959 Siemons ..75/ 10 3,550,671 12/1970 Harvey ..I64/52 OTHER PUBLICATIONS Electroslag Remelting, Medovar et al., JPRS 22217, 1963, pg. 168.

Primary Examiner-J. Spencer Overholser Assistant Examiner-John E. Roethel Attorney-Vincent G. Gioia and Robert F. Dropkin [57] ABSTRACT I A method for producing a metal ingot, which comprises the 13 Claims, No Drawings CONSUMABLE ELECTRODE MELTING USING A CENTRIFUGAL CAST ELECTRODE The present invention relates to a method for producing high quality metal and involves a sequence of steps which improves efficiency and reduces costs. It centers around a consumable electrode melting process and the use of a centrifugally cast electrode.

High quality metal is frequently prepared by consumable electrode melting processes which involve statically casting or forging of an electrode, remelting the electrode in a protective environment and casting of the remelted electrode into an ingot. The ingot produced is often characterized by a reduced incidence of non-metallic inclusions, less entrapped gases, less center porosity and segregation, improved hot workability and improved mechanical properties.

Metal manufacturers have been and are in search of less costly and more efficient consumable electrode melting processes. An answer to their search is furnished by the present invention. It provides a consumable electrode melting method which improves efficiency and reduces costs by employing centrifugally cast electrodes in place of statically cast electrodes.

The use of statically cast electrodes results in large yield losses from the melt to remelt stages whereas the use of centrifugally cast electrodes does not. Consumable electrode melting processes generally involve the welding of a stub to an electrode to render the electrode suitable for connection to a consumable electrode furnace clamp. The welding of a stub to a statically cast electrode however, involves a cutting operation, as statically cast electrodes have irregular ends. On the other hand, a cutting operation is not involved when a centrifugally cast electrode is welded to a stub as centrifugally cast electrodes have substantially flat ends. Cutting losses stemming from the use of statically cast electrodes may range from 5 to 12 percent.

Non-uniform melting and hot topping conditions result from the use of statically cast electrodes. The top .portion of a statically cast electrode contains a large portion of pipe. This pipe has an irregular configuration which causes erratic are conditions during electrode metal melting; i.e., remelting, and hot topping. Erratic are conditions cause aninterruption in the solidifying pattern and may damage the mold. Moreover, due to the unknown amount of pipe in the top portion of the electrode, it is impossible to establish a repetitive time for starting, operating and completing the hot top cycle. On the other hand, non-uniform melting and hot topping conditions are minimized with centrifugally cast electrodes as they are substantially devoid of pipe.

The use of statically cast electrodes can result in the production of a chemically segregated ingot. For example, the top section of a statically cast alloy tool steel consumable electrode has a lower carbon content than the remainder of the electrode and this segregation is carried over to the ingot when the electrode metal is subsequently melted; i.e., remelted. The loss of ingot material resulting from the segregation can be as high as percent. On the other hand, carbon segregation does not present a problem when alloy tool steel ingots are centrifugally cast.

it is accordingly an object of this invention to provide a consumable electrode melting process which reduces costs and improves efficiency.

It is a further object of this invention to provide a consumable electrode melting process which produces ingots of improved quality.

The present invention comprises the steps of: centrifugally casting metal into a consumable electrode; arranging the consumable electrode within a consumable electrode furnace structure; connecting the consumable electrode to a power supply; melting the consumable electrode in a protective environment by passing electrical current between it and a second electrode; and casting the molten metal into an ingot.

The consumable electrode is formed by centrifugally casting molten metal. Its formation is not, however, dependent upon any particular method of centrifugal casting as many suitable forms of centrifugal casting are embraced within the invention. Centrifugal casting is a pressure casting method in which the force of gravity for pouring molten metal into a mold is increased by spinning the mold assembly. Solidification proceeds from the crucible or mold wall to the center as the liquid metal is directed to and held on the crucible or mold wall by centrifugal force. The electrodes produced by centrifugal casting are characterized by being substantially uniform and devoid of pipe and by having substantially flat ends.

A consumable electrode furnace structure of any suitable or conventional design can be employed. Consumable electrode furnaces are well known in the art, are commercially available and form no part per se of this invention. The furnaces will ordinarily include means for controlling the gradual lowering of the electrode and a cooled crucible or mold.

Melting of the consumable electrode is performed in a protective environment. The environment can be an atmosphere of inert gas; e.g., helium or argon, a nitrogen atmosphere, a vacuum or a protective blanket layer of molten slag which covers the molten metal and the tip of the consumable electrode. Power for melting can be supplied from either direct or alternating current. Direct current can be either straight polarity; i.e., with the consumable electrode serving as cathode, or reverse polarity; i.e., with the consumable electrode serving as anode. The crucible or mold generally, but not necessarily, serves as the second electrode. A plurality of consumable electrodes can be used to increase efficiency. One setup employs three electrodes and three phase alternating current.

To obviate the need for welding a stub; i.e., a member which renders the electrode suitable for connection to a consumable electrode furnace clamp, to the consumable electrode, the method of the present invention can embrace the step of centrifugally casting the consumable electrode around the stub. The presence of pipe and/or unfavorable melting conditions makes it undesirable to incorporate this technique in static casting methods.

The method of this invention is particularly beneficial for producing alloy tool steel ingots. As stated earlier, the top section of a statically cast alloy tool steel consumable electrode has a lower carbon content than the remainder of the electrode. On the other hand, the carbon content of a centrifugally cast alloy tool steel consumable electrode is substantially uniform in the melting direction, i.e., the direction perpen dicular to that in which it solidified. The carbon segregation present in the statically cast electrode is carried over to the ingot when the electrode metal is subsequently melted; i.e., remelted. Losses of ingot material resulting from the segregation can be as high as 10 percent. Typical alloy tool steel compositions are found on page 1,095 of the Eighth Edition of The Making, Shaping and Treating of Steel, a book copyrighted in 1964 by United States Steel Corporation.

It will be apparent to those skilled in the art that the novel principles of the invention disclosed herein in connection with specific examples thereof will suggest various other modifications and applications of the same. It is accordingly desired that in construing the breadth of the appended claims they shall not be limited to the specific examples of the invention described herein.

We claim:

1. A method for producing a metal ingot, which comprises the steps of: centrifugally casting metal into a consumable electrode; arranging said consumable electrode within a consumable electrode furnace structure; connecting said consumable electrode to a power supply; melting said consumable electrode in a protective environment by passing electrical current between said consumable electrode and a second electrode; and casting said molten metal into an ingot.

2. A method according to claim 1 wherein said melting of said consumable electrode in a protective environment by passing electrical current between said consumable electrode and a second electrode comprises the step of passing direct current between said consumable electrode and said second electrode.

3. A method according to claim 2 wherein said consumable electrode serves as anode.

4. A method according to claim 2 wherein said consumable electrode serves as cathode.

5. A method according to claim 1 wherein said melting of said consumable electrode in a protective environment by passing electrical current between said consumable electrode and a second electrode comprises the step of passing alternating current between said consumable electrode and said second electrode.

6. A method according to claim 5 wherein three centrifugally cast consumable electrodes are melted with three phase alternating current.

7. A method according to claim 1 wherein said melting of said consumable electrode in a protective environment comprises the step of melting said consumable electrode in an inert atmosphere.

8. A method according to claim 1 wherein said melting of said consumable electrode in a protective environment comprises the step of melting said consumable electrode in a nitrogen atmosphere.

9. A method according to claim 1 wherein said melting of said consumable electrode in a protective environment comprises the step of melting said consumable electrode in a vacuum.

10. A method according to claim 1 wherein said melting of said consumable electrode in a protective environment comprises the step of melting said consumable electrode under a protective molten slag blanket.

11. A method according to claim 1 adapted to produce an alloy tool steel ingot.

12. A method according to claim 1 wherein said centrifugally cast electrode is cast around a member which renders the electrode suitable for connection to a consumable electrode furnace clamp.

13. A method for producing a metal ingot, which comprises the steps of: arranging a centrifugally cast metallic consumable electrode within a consumable electrode furnace structure; connecting said consumable electrode to a power supply; melting said consumable electrode in a protective environment by passing electrical current between said consumable electrode and a second electrode; and casting said molten metal into an ingot. 

1. A method for producing a metal ingot, which comprises the steps of: centrifugally casting metal into a consumable electrode; arranging said consumable electrode within a consumable electrode furnace structure; connecting said consumable electrode to a power supply; melting said consumable electrode in a protective environment by passing electrical current between said consumable electrode and a second electrode; and casting said molten metal into an ingot.
 2. A method according to claim 1 wherein said melting of said consumable electrode in a protective environment by passing electrical current between said consumable electrode and a second electrode comprises the step of passing direct current between said consumable electrode and said second electrode.
 3. A method according to claim 2 wherein said consumable electrode serves as anode.
 4. A method according to claim 2 wherein said consumable electrode serves as cathode.
 5. A method according to claim 1 wherein said melting of said consumable electrode in a protective environment by passing electrical current between said consumable electrode and a second electrode comprises the step of passing alternating current between said consumable electrode and said second electrode.
 6. A method according to claim 5 wherein three centrifugally cast consumable electrodes are melted with three phase alternating current.
 7. A method according to claim 1 wherein said melting of said consumable electrode in a protective environment comprises the step of melting said consumable electrode in an inert atmosphere.
 8. A method according to claim 1 wherein said melting of said consumable electrode in a protective environment comprises the step of melting said consumable electrode in a nitrogen atmosphere.
 9. A method according to claim 1 wherein said melting of said consumable electrode in a protective environment comprises the step of melting said consumable electrode in a vacuum.
 10. A method according to claim 1 wherein said melting of said consumable electrode in a protective environment comprises the step of melting said consumable electrode under a protective molten slag blanket.
 11. A method according to claim 1 adapted to produce an alloy tool steel ingot.
 12. A method according to claim 1 wherein said centrifugally cast electrode is cast around a member which renders the electrode suitable for connection to a consumable electrode furnace clamp.
 13. A method for producing a metal ingot, which comprises the steps of: arranging a centrifugally cast metallic consumable electrode within a consumable electrode furnace structure; connecting said consumable electrode to a power supply; melting said consumable electrode in a protective environment by passing electrical current between said consumable electrode and a second electrode; and casting said molten metal into an ingot. 